Creating a fake-weld to stick the gun to the arm? (whilst it's actually m6d'ed to the HRP)

Animating with the gun attached to the hand as such removes a lot of the pain of tracking the gun’s handle to the hand, however, it’s essential I have the gun itself M6D to the HRP of the rig, is there a way I can create a fake weld inside of the animation editor so the gun attaches to the arm yet the animation will function with the HRP binded motor 6d?

What I wish to achieve:

What I currently have:

Just wondering if there’s something I’m missing, any help is appreciated.